1. Field of the Invention
The present invention relates to a method for stabilizing the output of a rain sensor for use in controlling the driving of a wiper, and to a protection method for the rain sensor for preventing malfunction thereof due to an increase or decrease in ambient temperature.
2. Description of Prior Art
As a conventional controller apparatus utilizing a rain sensor, a wiper controller apparatus of the water drop sensitive-type as disclosed in Japanese Patent Laying-Open No. Hei 2-67945 (1990) is already known. In this prior art document, light means (i.e., light emitting means) and detection means (i.e., light receiving means) are positioned upon an inside surface of a window glass, opposing to each other at a distance, within a wiping area of a wiper wiping an outside surface of the window glass, and the adhesion or presence of the water drops upon the outside surface of the window glass is decided or detected on the basis of a difference between output signal levels generated from the detection means before and after driving of the wiper, so as to drive the wiper.
However, in the conventional wiper controller apparatus of water drop sensitive-type, the output signal from the light receiving means fluctuates in the following cases although no water is adhered to or present upon the outside surface of the window glass, for instance, when the outside surface of the window glass is soiled or dirty, when the emitted output light is changed for any reason (such as change or deterioration of a light emitting source with the passage of time or age, etc.), when amplification factor(s) of circuit(s) is/are changed due to the fluctuation of ambient temperature, and further when noise from the outside affect the device.
Accordingly, it has a drawback in that the wiper, in those cases mentioned above, is sometimes driven though it is not necessary since the light receiving means erroneously outputs a signal as if the water drops are adhered or present upon the outside surface of the window glass.
Further, another wiper controller apparatus of the water drop sensitive-type is also known wherein the light emitting means and the light receiving means are positioned on an inside surface of the window glass opposing to each other at a distance within the wiping area of the wiper wiping the outside surface of the window glass, and the adhesion or presence of the water drops upon the outside surface of the window glass is decided or detected on the basis of a difference between output signal levels from the detection means before and after the driving of the wiper, so as to drive the wiper.
However, this conventional wiper controller apparatus of the water drop sensitive-type also has a drawback in that malfunctions can occur in various circuits or in that the light emitting element, such as a laser diode (LD), can be damaged since a rain sensor is always under the condition of driving, not only when it rains but also under bright sunshine when no wiper is needed to be driven.
Further, there is also a possibility that the wiper may become frozen and then is non-operable under sub-zero ambient temperatures, and therefore it has other drawbacks in that excessive driving current flows through the wiper driving motor if the rain sensor is switched to the driving condition, resulting in the driving motor being burned out.
For resolving the above-mentioned drawbacks, according to the present invention, there is provided a method for stabilizing the output of a rain sensor for a wiper driver apparatus, said rain sensor comprising light emitting means for guiding light into a window glass so as to undergo total internal reflection within said window glass; light receiving means having an amplifier circuit and for receiving the light which has undergone total internal reflection within said window glass; and, means for detecting the amount of water drops adhered or present upon an outside surface of said window glass based on an output signal of said light receiving means and for outputting a driving signal to the wiper driver apparatus, wherein said method comprises:
applying power from an electric power source to the rain sensor;
obtaining a difference signal corresponding to a difference between a preset reference value and the output signal of the amplifier circuit of said light receiving means;
feeding said difference signal back to said amplifier circuit; and
adjusting an amplification factor of said amplifier circuit so as to maintain the output signal of said amplifier circuit at a constant value.
With this method, when power has been applied to the rain sensor from an electric power source, a difference signal corresponding to the difference between a preset reference value and an output signal of the amplifier circuit of the light receiving means is obtained and is fed back to the amplifier, and further the amplification factor of the amplifier circuit is adjusted so as to maintain the output signal thereof at a constant value, irrespective of the operation condition of the wiper. Therefore, the output signal of the amplifier circuit is always maintained at a constant value, thereby ensuring no decrease in sensitivity in the following cases, that is, when the window glass is soiled or dirty upon the outside surface thereof, when a fluctuation occurs in the output light which is received by the light receiving means for any reason, when the amplification factor(s) of circuit(s) is/are changed due to fluctuations in the ambient temperature, and when externally generated noise is present, and so on.
Further, according to the present invention, there is also provided a protection method for a rain sensor comprising light emitting means for guiding light into a window glass so as to undergo total internal reflection within said window glass; light receiving means for receiving the light which has undergone total internal reflection within said window glass; and means for detecting the amount of water drops adhered or present upon an outside surface of said window glass based on an output signal of said light receiving means, wherein said method comprises:
measuring a driving current supplied to said light emitting means;
converting the driving current into a value corresponding to the ambient temperature; and
stopping supply of the driving current to said light emitting means when said converted value of ambient temperature exceeds a preset higher temperature.
With this method, by selecting the preset higher temperature value at a temperature corresponding to the condition of bright, hot sunshine when no wiper operation is needed, the rain sensor is saved from any damage to the light emitting element, comprising, for example, a laser diode (LD), and from any malfunctions of various circuits thereof, since it remains in a non-driving condition when the ambient temperature exceeds the preset higher temperature value.
Further, according to the present invention, there is also provided a protection method for a rain sensor comprising light emitting means for guiding light into a window glass so as to undergo total internal reflection within said window glass: light receiving means for receiving the light which has undergone total internal reflection within said window glass; and means for detecting the amount of water drops adhered or present upon an outside surface of said window glass based on an output signal of said light receiving means, wherein said method comprises:
measuring a driving current supplied to said light emitting means;
converting the driving current into a value corresponding to the ambient temperature; and
stopping supply of the driving current to said light emitting means when said converted value of the ambient temperature is less than a preset lower temperature.
With this method, by selecting the preset lower temperature value at a temperature corresponding to a few xc2x0C. where freezing will not occur, the driving motor of the wiper is saved from burn-out caused by excessive driving current flowing therethrough in the case where the wiper blade is inoperable due to the freezing thereof, since the rain sensor remains in a non-driving condition until the ambient temperature reaches the preset lower temperature.
Moreover, according to the present invention, there is further provided a protection method for a rain sensor comprising light emitting means for guiding light into a window glass so as to undergo total internal reflection within said window glass; light receiving means for receiving the light which has undergone total internal reflection within said window glass; and means for detecting the amount of water drops adhered or present upon an outside surface of said window glass based on an output signal of said light receiving means, a temperature detecting element being provided in the vicinity of said rain sensor, wherein said method comprises:
obtaining an output signal from said temperature detecting element; and
stopping supply of a driving current to said light emitting means when said output signal of said temperature detecting element exceeds a preset higher temperature.
With this method, by selecting the preset higher temperature value at a temperature corresponding to the situation of bright, hot sunshine, where no wiper operation is needed, the rain sensor is protected from damage to its light emitting element, comprising, for example, a laser diode (LD), and is protected from malfunctions of various circuits thereof, since the device remains in the non-driving condition when the ambient temperature exceeds the preset higher temperature value.
Furthermore, according to the present invention, there is also provided a protection method for a rain sensor comprising light emitting means for guiding light into a window glass so as to undergo total internal reflection within said window glass; light receiving means for receiving the light which has undergone total internal reflection within said window glass; and means for detecting the amount of water drops adhered or present upon an outside surface of said window glass based on an output signal of said light receiving means, a temperature detecting element being provided in the vicinity of said rain sensor, wherein said method comprises:
obtaining an output signal from said temperature detecting element; and
stopping supply of a driving current to said light emitting means when said output signal of said temperature detecting element is less than a preset lower temperature.
With this method, by selecting the preset higher temperature value at a temperature corresponding to a few xc2x0C. where freezing will not occur, the driving motor of the wiper is saved from burn-out caused by any excessive driving current flowing therethrough in the case where the wiper blade is inoperable due to the freezing thereof, since the rain sensor is in the non-driving condition until the ambient temperature reaches the preset lower temperature value.
Further, according to the present invention, in the protection method for a rain sensor as mentioned above, the higher preset temperature value and lower preset temperature value can be freely adjusted in advance.
With the higher preset temperature value and lower preset temperature value being freely adjustable, they can be preset depending upon local environmental conditions under which the rain sensor will be used.